During the rinse step of a dishwashing cycle, fresh water is sprayed onto the dishware to rinse food soils and detergent from the surface of the dishware. When the fresh water is relatively low in dissolved solids (i.e., minerals in the water), the dishware appears substantially film-free and spot-free after it dries. However, when the fresh water contains high levels of dissolved solids, the dried dishware can have a significant amount of visible film and spots due to the minerals in the water. The solids remain on the dishware after the water evaporates, leaving behind rather unsightly film and spots, especially on glassware, flatware, and dark-colored dishware items.
Reverse osmosis is an effective mechanism for removing dissolved solids from water in areas that have high levels of dissolved solids in the water. However, reverse osmosis systems by nature waste water because to maintain the membrane of the system in functional working condition, the membrane surface is periodically flushed with water, which is subsequently discarded. The concentrate (wastewater) is passed at high flow rates across the membrane surface to remove solids from the surface to prevent the membrane from getting plugged and fouled. If 100% of the water were forced through the membrane, the membrane life would be reduced and the flow of water (production of permeate) would be severely reduced. Therefore, the most efficient way to operate a reverse osmosis system is to waste a certain amount of water.
There are various ways to reduce the amount of wastewater from a reverse osmosis system, including recycling the concentrate water back to the reverse osmosis feed and using multiple membranes in series. However, for practical purposes, the reverse osmosis system will still create some wastewater. In the current state of the art for a commercial reverse osmosis system, a ratio of about 50% permeate to about 50% concentrate has been found to provide an effective balance for allowing a reverse osmosis system to operate in a wide variety of water conditions while minimizing the amount of equipment involved in the overall system.